JPH0954977A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce two kinds of optical recording media in which optimum wavelengthes of semiconductor lasers for reproducings and numerical aperrtures of objective lenses are different. SOLUTION: In an optical system in which a first light having a first wavelength from a module 11 and a second light having a second wavelength from a module 12 are multiplexed in a wavelength filter 13 to be condensed on a disk 17 by a collimator lens 14 and an objective lens 16 and then they are reflected, a numerical aperture limiting element 15 is provided in between the collimator lens 14 and the objective lens 16. The numerical aperture limiting element 15 allows an incident light to be totally transmitted with respect to the first light having the first wavelength from the module 11 and allows only the center part of the cross section of the luminous flux of an incident light to be transmitted with respect to the second light having the second wavelength from the mudule 12. Consequently, the effective numerical apertures of the objective lens 16 are made different in correspondence with two wavelengths.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device, and more particularly to an optical head device for recording and reproducing on two different types of optical recording media.

[0002]

2. Description of the Related Art In recent years, standardization of digital video discs having a larger capacity than compact discs has been promoted. FIG. 18 is a block diagram showing an example of a conventional optical head device used for reproducing the digital video disc and the compact disc. In the figure, a semiconductor laser 190
The light emitted from is incident on the half mirror 191, where about half is reflected, and the reflected light is further reflected by the collimator lens 1.
After being collimated by 4, the objective lens 16 is used for the disc 17
The light is condensed on the upper side to form a spot and then reflected.

The reflected light from the disk 17 is the objective lens 1
6. The light is transmitted through the collimator lens 14 in the opposite direction to the light incident direction and is incident on the half mirror 191. About half of the light is transmitted here, and the transmitted light is further irradiated to the photodetector 193 via the concave lens 192 and received. To be done. The photodetector 193 has a four-divided light receiving section and outputs a focus error signal to the half mirror 1.
The astigmatism method using the astigmatism generated at 91 is detected, and the track error signal is detected by the push-pull method. Further, the reproduction signal is detected from the sum of the output signals of the four-division light receiving section of the photodetector 193.

[0004]

In order to reproduce a large-capacity digital video disc, it is necessary to reduce the diameter of the focused spot on the disc surface corresponding to the narrow track pitch. Since the diameter of the focused spot is inversely proportional to the numerical aperture of the objective lens 16 and proportional to the wavelength of light, the objective lens 1
The numerical aperture of 6 must be increased to about 0.52 to 0.6, and the wavelength of the emitted light of the semiconductor laser 190 must be shortened to about 635 nm to 655 nm.

On the other hand, in order to reproduce a compact disc, the compact disc has a loose standard with respect to the disc tilt and it is necessary to suppress the occurrence of coma aberration due to the disc tilt. Therefore, the numerical aperture of the objective lens 16 is about 0.45. And have to lower it. Further, in order to reproduce a write-once compact disc (CD-R) which is a kind of compact disc and which uses an organic dye as a recording medium, the write-once compact disc is 70% or more only for incident light near a wavelength of 785 nm. The wavelength of the emitted light of the semiconductor laser 190 must be about 785 nm because it is designed to obtain a high reflectance.

As described above, the two types of optical recording media, that is, the digital video disc and the compact disc including the write-once type, differ in the optimum wavelength of the semiconductor laser for reproducing each and the numerical aperture of the objective lens. It is impossible for the conventional optical head device shown in (1) to reproduce two types of optical recording media.

[0007] The present invention has been made in view of the above points,
An object of the present invention is to provide an optical head device capable of reproducing two types of optical recording media such as a digital video disc and a compact disc including a write-once type.

[0008]

To achieve the above object, the present invention provides a first light source for emitting a first light of a first wavelength and a second light source of a second wavelength different from the first wavelength. A second light source for emitting a second light, a first light from the first light source and a second light source
Second light from the light source is guided to the optical recording medium, while it is multiplexed by the optical multiplexing / demultiplexing means and the optical multiplexing / demultiplexing means for demultiplexing the reflected light from the optical recording medium. Is provided between the objective lens that reflects the reflected light on the optical recording medium after condensing the collected light on the optical recording medium and transmits the reflected light, and the optical multiplexing / demultiplexing means and the objective lens. All the light is transmitted,
An aperture limiting element that transmits only the central portion of the cross section of the light flux of the incident light of the second wavelength, and a first photodetection optical system that receives the reflected light of the first wavelength that is demultiplexed by the optical multiplexing / demultiplexing means. ,
The second optical detection optical system receives the reflected light of the second wavelength that is demultiplexed by the optical multiplexing / demultiplexing means.

Further, the aperture limiting element in the present invention includes a wavelength filter film provided only outside a circular region having a diameter smaller than the effective diameter of the objective lens on the substrate, and a phase filter provided on the wavelength filter film. The first light of the first wavelength is almost completely transmitted outside the circular region, the second light of the second wavelength is almost completely reflected outside the circular region, and the light incident on the circular region is formed. Is characterized in that the first and second lights are completely transmitted.

Further, the aperture limiting element in the present invention comprises a diffraction grating formed on the substrate only outside the circular region having a diameter smaller than the effective diameter of the objective lens, and the diffraction grating has the first wavelength of the first wavelength. The first light is completely transmitted, the second light of the second wavelength is almost diffracted, and the light incident on the circular region is completely transmitted by both the first and second lights. To do.

Further, in the aperture limiting element according to the present invention, the diffraction grating and the wavelength filter film are formed on the first substrate, and the phase compensation film is formed on the second substrate in a circular shape having a diameter smaller than the effective diameter of the objective lens. It is sequentially laminated only on the outside of the region, the space between the second substrate and the wavelength filter film is filled with an adhesive, and the first light of the first wavelength is completely transmitted outside the circular region, It is characterized in that the second light of the second wavelength is completely reflected and diffracted, and the light incident on the circular region is completely transmitted by both the first and second lights.

The optical head device according to the present invention combines the first light from the first light source and the second light from the second light source and guides them to the optical recording medium, while An aperture limiting element is provided between the optical multiplexing / demultiplexing means for splitting the reflected light and the objective lens.
All of the incident light is transmitted with respect to the first light of the wavelength, and only the central portion of the cross section of the incident light is transmitted with respect to the second light of the second wavelength from the second light source. As a result, the objective lens can be used for the first light with an effective numerical aperture determined by the effective diameter of the objective lens and the focal length of the objective lens, and the second light can pass through the aperture limiting element. The objective lens can be used with an effective numerical aperture determined by the diameter of the cross section of the luminous flux and the focal length of the objective lens.

That is, in the present invention, since the effective numerical aperture of the objective lens is made to correspond to the two wavelengths, the optimum wavelength and the numerical aperture of the objective lens for each of the two types of optical recording media are set. Can be selected.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of a first embodiment of an optical head device according to the present invention. In the figure, the module 11 and the module 12 are equipped with a semiconductor laser and a detection optical system for receiving the reflected light from the disk 17. The wavelength of the semiconductor laser in the module 11 is 635 nm, and the wavelength of the semiconductor laser in the module 12 is 785 nm. The wavelength filter 13 has a wavelength of 635
nm light is almost completely transmitted, and light having a wavelength of 785 nm is almost completely reflected. Therefore, the light emitted from the semiconductor laser in the module 11 is emitted by the wavelength filter 13
Of light emitted from the semiconductor laser in the module 12 is reflected by the wavelength filter 13 with almost no loss.

The light emitted from the semiconductor laser in the module 11 which has passed through the wavelength filter 13 with almost no loss is collimated by the collimator lens 14, and after passing through the aperture limiting element 15 having a structure described later, the objective lens 16 is formed. Is focused on the disk 17 to form a spot and then reflected.
The reflected light from the disk 17 passes through the objective lens 16, the aperture limiting element 15, and the collimator lens 14 in the opposite direction, passes through the wavelength filter 13, and then is received by the detection optical system in the module 11.

On the other hand, the light emitted from the semiconductor laser in the module 12 which is reflected by the wavelength filter 13 with almost no loss is collimated by the collimator lens 14 and only the central portion of the cross section of the light flux passes through the aperture limiting element 15. After that, the light is focused on the disk 17 by the objective lens 16, forms a spot, and is reflected. The reflected light from the disk 17 passes through the objective lens 16, the aperture limiting element 15, and the collimator lens 14 in the opposite direction, is reflected by the wavelength filter 13, and then is received by the detection optical system in the module 12. The aperture limiting element 15 and the objective lens 16 are integrally driven by an actuator.

FIG. 2A is a plan view of the aperture limiting element 15 of FIG. 1, and FIG. 2B is a sectional view taken along line II-II of FIG. As shown in FIGS. 3A and 3B, the aperture limiting element 15 has a substantially flat rectangular shape and a wavelength filter film 22 and a phase compensation film 23 are laminated on a glass substrate 21, which is transparent to light. The circular groove 20 is formed in the center of the plate having the above structure. The diameter 2b of the circular groove 20 is smaller than the effective diameter 2a of the objective lens 16.

The wavelength filter film 22 functions to almost completely transmit light having a wavelength of 635 nm and almost completely reflect light having a wavelength of 785 nm. Further, the phase compensation film 23 is
For the wavelength of 635 nm, the phase difference between the light passing through the wavelength filter film 22 and the phase compensation film 23 and the light passing through the air is 2π.
[Rad. ] To adjust. That is, the aperture limiting element 15 completely transmits light having a wavelength of 635 nm and completely reflects light having a wavelength of 785 nm in portions other than the circular groove 20 having a diameter of 2b, and has a wavelength of 635 nm in the circular groove 20 having a diameter of 2b. It also completely transmits light of 785 nm.

The wavelength filter film 22 has a structure in which, for example, an odd number of high refractive index layers and low refractive index layers are alternately deposited on the glass substrate 21. In order to provide the above wavelength selection characteristics, when the high refractive index layer and the low refractive index layer have refractive indices n ₁ and n ₂ and thicknesses d ₁ and d ₂ , n ₁ · d ₁ = n ₂ · d ₂ = λ / 4 (λ =
785 [nm]). Ti as high refractive index layer
If O ₂ and SiO ₂ are used as the low refractive index layer, n ₁ = 2.
Since 30 and n ₂ = 1.46, d ₁ = 85 from the above formula.
[Nm] and d ₂ = 134 [nm]. On the other hand, the phase compensation film 23 can be produced by depositing SiO ₂ on the wavelength filter film 22, for example.

The second embodiment of the optical head device of the present invention has a configuration in which the aperture limiting element 15 shown in FIG. 2 is replaced by the aperture limiting element 25 shown in FIG. 3 in the configuration diagram of FIG.
FIG. 3A shows the aperture limiting element 2 used in the second embodiment.
5 is a plan view of FIG. 5, and FIG. 3 (b) is III-III of FIG.
FIG. 3 shows a sectional view along the line. As shown in FIGS. 3A and 3B, the aperture limiting element 25 has a rectangular plane and a diffraction grating 29 on a glass substrate 28 that is transparent to light.
The circular groove 27 is formed at the center of the plate having the structure. The diameter 2b of the circular groove 27 is smaller than the effective diameter 2a of the objective lens 16.

The diffraction grating 29 is an S on the glass substrate 28.
It is manufactured by deposition of iO ₂ , etching of the glass substrate 28, integral molding of glass or plastic, and the like. When the thickness of the diffraction grating 29 is h, the refractive index is n, and the wavelength of incident light is λ, the transmittance is cos ² (φ / 2) (where φ = 2π
(N-1) h / λ). Therefore, for example, the thickness h of the diffraction grating 29 is 4.14 μm, and the refractive index n is 1.46.
Then, when the wavelength λ of the incident light is 635 nm, φ = 6
Since it is π, the transmittance is 100%, and when λ is 785 nm, φ = 4.85π, and therefore the transmittance is 5.4%.

That is, the aperture limiting element 25 has a circular groove 27.
In the peripheral portion (portion other than the circular groove 27), the wavelength 63
The light of 5 nm is completely transmitted, and the light of 785 nm wavelength is almost diffracted.
The light of 5 nm and 785 nm is completely transmitted. The pattern of the diffraction grating 29 may have another shape such as a concentric shape instead of a straight shape.

The third embodiment of the optical head device of the present invention has a configuration in which the aperture limiting element 15 shown in FIG. 2 is replaced by the aperture limiting element 31 shown in FIG. 4 in the configuration diagram of FIG.
FIG. 4A shows the aperture limiting element 3 used in the third embodiment.
1 is a plan view, and FIG. 4B is a sectional view taken along the line IV-IV in FIG.

As shown in FIGS. 4 (a) and 4 (b), the aperture limiting element 31 has a substantially flat rectangular shape, and a diffraction grating 35 and a wavelength filter film are formed on a glass substrate 34 which is transparent to light. 36, the glass substrate 38, and the phase compensation film 39 at the center of the plate having a structure in which the phase compensation film 39 is laminated.
In addition, the circular groove 33 is formed. This circular groove 3
The diameter 2b of 3 is smaller than the effective diameter 2a of the objective lens 16. The diffraction grating 35 and the wavelength filter film 36 are provided with a central hole having a diameter of 2b at the center.

The phase compensation film 39 is formed on the glass substrate 38, and the space between the wavelength filter film 36 and the glass substrate 38 is filled with an adhesive 37. Wavelength filter film 36
Transmits almost completely the light of wavelength 635 nm,
It has the property of almost completely reflecting the light of 85 nm. Further, the phase compensation film 39 has a phase difference of 2π between the light passing through the diffraction grating 35, the wavelength filter film 36, and the phase compensation film 39 and the light passing through the adhesive 37 and the air for a wavelength of 635 nm.
[Rad. ] To adjust.

The diffraction grating 35 is formed on the glass substrate 34 by S
deposition of iO _2, the etching of the glass substrate 34 is manufactured by integrally molding a glass or plastic. It does not act as a diffraction grating for the transmitted light of the wavelength filter film 36, and for the reflected light of the wavelength filter film 36, the thickness of the diffraction grating 35 is h, the refractive index is n, and the wavelength of the incident light is λ. Then, the reflectance is cos ² (φ / 2) (where φ = 4πnh /
λ). For example, h = 134 nm, n = 1.4
In the case of 6, since Φ = π for λ = 785 nm, the reflectance is 0%.

That is, in the aperture limiting element 31, the portion around the circular groove 33 having the diameter 2b (the portion other than the circular groove 33) completely transmits the light having the wavelength of 635 nm and the wavelength 785.
The light of nm is completely reflected and diffracted, and the circular groove 33 having a diameter of 2b is used.
Inside, light of wavelengths 635 nm and 785 nm is completely transmitted.

The wavelength filter film 36 is, for example, the diffraction grating 3
5 can be produced by alternately depositing a high-refractive index layer and a low-refractive index layer on top of No. 5. In order to make the above function work, the refractive indices of the high refractive index layer and the low refractive index layer are n ₁ , n ₂ and the thickness is
_{When 1} and d ₂ , n ₁ · d ₁ = n ₂ · d ₂ = λ / 4 (λ = 7
85 [nm]). TiO as a high refractive index layer
₂ , using SiO ₂ as the low refractive index layer, n ₁ = 2.3
Since 0 and n ₂ = 1.46, d ₁ = 85 [nm], d ₂
= 134 [nm].

On the other hand, the phase compensation film 39 can be produced by depositing SiO ₂ on the glass substrate 38, for example. As the adhesive 37, a material having a refractive index substantially the same as that of the diffraction grating 35 is used. Further, the pattern of the diffraction grating 35 may be other shapes such as a concentric shape instead of a straight shape.

The wavelengths 635 nm and 785 of the aperture limiting elements 15, 25 and 31 shown in FIGS. 2, 3 and 4, respectively.
The effective numerical aperture for light of nm is given by a / f and b / f, respectively, where f is the focal length of the objective lens 16. For example, f = 3 [mm], a = 1.56 [m
m] and b = 1.35 [mm], a / f = 0.5
2, b / f = 0.45. Therefore, the wavelength is 635 nm
It is possible to reproduce a digital video disc with a combination of a numerical aperture of 0.52 and a numerical aperture of 0.52, and to reproduce a compact disc including a write-once type with a combination of a wavelength of 785 nm and a numerical aperture of 0.45. The present invention can be applied not only to the read-only type and the write-once type but also to the rewritable type phase change disk and the magneto-optical disk. The aperture limiting elements 15, 25 and 31 can also be integrated with the objective lens 16.

Next, the structure of the wavelength filter used in the embodiment of the optical head device of the present invention will be described. FIG. 5 shows a configuration diagram of each example of the wavelength filter. The wavelength filter 13 shown in FIG. 5A is formed by bonding two glass blocks 41 and 42 via a dielectric multilayer film 43. As shown in FIG. 5A, the incident light 44 having a wavelength of 635 nm is incident on the dielectric multilayer film 43 at an incident angle of 45 degrees, is almost completely transmitted, and travels straight. On the other hand, the incident light 45 having a wavelength of 785 nm enters the dielectric multilayer film 43 at an incident angle of 45 degrees, is almost completely reflected, and the traveling direction is bent by 90 degrees.

In the wavelength filter 47 shown in FIG. 5B, blocks 48 and 49 of the three glass blocks 48, 49 and 50 are bonded together via a dielectric multilayer film 51, and the blocks 49 and 50 are combined. The dielectric multilayer film 52 is used for bonding. As shown in FIG. 5B, the incident light 44 having a wavelength of 635 nm is incident on the dielectric multilayer film 52 through the block 50 at an incident angle of 22.5 degrees, is almost completely transmitted, and is transmitted through the block 49. Go straight. On the other hand, as shown in FIG. 5B, the incident light 45 having a wavelength of 785 nm enters the dielectric multilayer film 51 through the block 49 at an incident angle of 22.5 degrees, and after being reflected almost completely here. , Is incident on the dielectric multilayer film 52 at an incident angle of 22.5 degrees, and is reflected almost completely also here, the traveling direction is 9
It is bent at 0 ° and emitted through the block 49. Generally, the wavelength filter is easier to design as the incident angle to the dielectric multilayer film is smaller.

The wavelength filter 1 shown in FIGS. 5 (a) and 5 (b).
Dielectric multilayer films 43, 51 and 52 used in 3, 47
Is designed to almost completely transmit the incident light 44 having a wavelength of 635 nm and almost completely reflect the incident light 45 having a wavelength of 785 nm. However, it transmits almost completely the light having a wavelength of 785 nm and transmits the light having a wavelength of 635 nm. Can also be designed to reflect almost completely. in this case,
The wavelength of the semiconductor laser in the module 11 of FIG.
nm, the wavelength of the semiconductor laser in the module 12 is 635
nm may be changed respectively.

If the polarization direction of the light emitted from the semiconductor laser and the polarization direction of the reflected light from the disk are the same, a polarization beam splitter can be used instead of the wavelength filter. For example, wavelengths of 635 nm and 785 nm
By making the light of (1) enter the polarization beam splitter as P-polarized light and S-polarized light, respectively, the former is almost completely transmitted and the latter is almost completely reflected.

Next, a module when the optical head device of the present invention is applied to an optical head device for a read-only type disk will be described. FIG. 6 shows a block diagram of an example of the module in this case. As shown in the figure, in this module, a spacer 59 is sandwiched between a package 56 accommodating a semiconductor laser 54 and a photodetector 55 and a window portion of the package 56 in the optical path of laser light emitted from the semiconductor laser 54. Diffraction grating 57 and hologram optical element 58 provided
It is composed of The diffraction grating 57 and the hologram optical element 58 have a structure in which a pattern is formed of SiO ₂ on a glass substrate, and have a function of transmitting a part of incident light and diffracting a part thereof.

Next, the operation of this module will be described. The laser light emitted from the semiconductor laser 54 travels straight and is divided by the diffraction grating 57 into three lights, that is, the transmitted light and the ± first-order diffracted light. About 50% of element 58
Permeate through to the disc (not shown). The three lights reflected by the disc are respectively holographic optical elements 58.
Is incident on the photodetector 55 and is then diffracted by about 40% as ± first-order diffracted light, transmitted through the diffraction grating 57 and received by the photodetector 55.

FIG. 7 shows each example of the mounting form of the semiconductor laser 54 on the photodetector 55 in the module of FIG. FIG. 7A shows the case where a glass mirror is used. The semiconductor laser 54 is installed on the photodetector 55 via a heat sink 61. The light emitted laterally from the semiconductor laser 54 is reflected by the inclined surface of the glass mirror 62 and travels upward in the drawing.

Further, FIG. 7B shows the case where a mirror formed by etching is used for the photodetector 55. The photodetector 55 has a concave portion 63 and a mirror 64 with an inclined surface formed by etching in the upper portion, and the semiconductor laser 54 is installed in the concave portion 63 formed by etching in the photodetector 55. As a result, the light emitted laterally from the semiconductor laser 54 is reflected by the mirror 64 formed by etching in the photodetector 55 and travels upward in the drawing.

FIG. 8A shows an interference fringe pattern of the diffraction grating 57 in the module of FIG. 6, and FIG. 8B shows an interference fringe pattern of the hologram optical element 58 in the module of FIG. The diffraction grating 57 has a pattern only in a region 66 near the center. The light emitted from the semiconductor laser 54 passes through the inside of the area 66, and the light reflected from the disk is emitted in the area 6.
Pass outside 6.

The hologram optical element 58 is shown in FIG.
As shown in (b), it has an off-axis concentric circular pattern, and functions as a convex lens for + 1st-order diffracted light and as a concave lens for -1st-order diffracted light.

FIG. 9 shows the photodetector 55 in the module of FIG.
An example of the pattern of the light receiving part and the arrangement of the light spots on the light receiving part are shown. In FIG. 9, a semiconductor laser 54 is provided at a position slightly below the center of the photodetector 55, and a mirror 70 for reflecting the emitted light of the semiconductor laser 54 is provided. Further, in the figure with the installation position of the mirror 70 sandwiched,
Light receiving portions 71, 72 and 73 are arranged on the left side, and light receiving portions 74, 75 and 76 are arranged on the right side. Furthermore,
On the upper side of the light receiving units 71 and 74 in the drawing, the light receiving units 77 and 7
8 are provided, and light receiving portions 79 and 80 are provided on the lower side of the light receiving portions 73 and 76 in the figure, respectively. Light receiving parts 71, 7
2 and 73 total light receiving area and light receiving portions 74, 75 and 7
The light receiving area of the entire 6 is the same, and the light receiving portions 77, 78, 79
And 80 are almost the same as the light receiving areas.

Of the transmitted light on the outward path of the diffraction grating 57 shown in FIG. 6, the + 1st order diffracted light of the hologram optical element 58 on the return path forms a light spot 81 on the three-divided light receiving portions 71 to 73 shown in FIG. The -1st-order diffracted light of the hologram optical element 58 formed on the return path forms a light spot 82 on the three-divided light receiving portions 74 to 76. Of the + 1st order diffracted light on the outward path of the diffraction grating 57, the ± 1st order diffracted light on the backward path of the hologram optical element 58 forms light spots 83 and 84 on the light receiving portions 77 and 78, respectively. Of the −1st order diffracted light, the ± 1st order diffracted light of the hologram optical element 58 on the return path is reflected by the light spot 8 on the light receiving portions 79 and 80, respectively.
5, 86 are formed.

The light receiving parts 71 to 73, 77 and 79 are located behind the converging point, and the light receiving parts 74 to 76, 78 and 80 are located in front of the converging point. When the levels of the electric signals obtained by photoelectric conversion by the light receiving units 71 to 80 are represented by V71 to V80, the focus error signal is {(V71 + V73 +) by the known spot size method.
V75)-(V72 + V74 + V76)}, and the track error signal is obtained by the known 3-beam method.
It is obtained from the calculation of {(V77 + V78)-(V79 + V80)}. The reproduction signal of the disc is (V71 +
V72 + V73 + V74 + V75 + V76).

Next, a module when the optical head device of the present invention is applied to an optical head device of a write-once disc or a rewritable phase change disc will be described. FIG. 10 shows a block diagram of an example of the module in this case. As shown in the figure, this module includes a semiconductor laser 90, a package 92 accommodating a photodetector 91, and a semiconductor laser 90.
The polarizing hologram optical element 93 and the quarter-wave plate 94 provided in the window portion of the package 92 in the optical path of the emitted laser light.

The polarizing hologram optical element 93 is shown in FIG.
As shown in FIG. 3, a pattern is formed on the lithium niobate substrate 96 having birefringence by the proton exchange region 97 and the phase compensation film 98, and all the ordinary light of the incident light is transmitted and all the extraordinary light is transmitted. It works to diffract.

Next, the operation of the module shown in FIG. 10 will be described. The emitted light from the semiconductor laser 90 is incident on the polarizing hologram optical element 93 as ordinary light and is transmitted therethrough. The polarized light is converted into circularly polarized light and goes to a disk (not shown). The reflected light from the disc is incident on the quarter-wave plate 94 and converted from circularly polarized light to linearly polarized light, and then is incident on the polarizing hologram optical element 93 as extraordinary light. The light is diffracted and received by the photodetector 91. The mounting form of the semiconductor laser 90 on the photodetector 91 is similar to that shown in FIG.

FIG. 12 shows a pattern of interference fringes of the polarizing hologram optical element 93. As shown in the figure, the polarization hologram optical element 93 is divided into four regions 101 to 104. The optical axis 105 of the polarization hologram optical element 93 is set in the direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 90.

FIG. 13 shows an example of the pattern of the light receiving part of the photodetector 91 of the module shown in FIG. 10 and the arrangement of the light spots on the light receiving part. In FIG. 13, the semiconductor laser 90 is provided at a position slightly below the center of the photodetector 91, and
Mirror 10 for reflecting emitted light of semiconductor laser 90
7 are provided. Further, in the figure, the light receiving portions 109 and 11 divided into two parts on the left side of the installation position of the mirror 107.
0 is also divided into two light receiving portions 111 and 112 on the right side.
Are arranged respectively. Further, the light receiving units 109 and 11
1, the light receiving portions 113 and 114 are provided on the upper side in the drawing, and the light receiving portions 115 and 116 are provided on the lower side in the drawing of the light receiving portions 110 and 112, respectively.

The + 1st order diffracted light from the region 101 of the polarization hologram optical element 93 shown in FIGS. 10 and 12 forms a light spot 118 on the dividing line of the two light receiving portions 109 and 110 as shown in FIG. The −1st order diffracted light from the region 101 forms a light spot 122 on the light receiving portion 116. The + 1st-order diffracted light from the region 102 in FIG. 12 of the polarizing hologram optical element 93 is 2 as shown in FIG.
A light spot 119 is formed on the dividing line of the divided light receiving portions 111 and 112, and the −1st order diffracted light from the region 102 forms a light spot 123 on the light receiving portion 115.

The ± 1st-order diffracted light from the region 103 of the polarizing hologram optical element 93 shown in FIG.
12, light spots 120 and 124 are formed on the light receiving portions 113 and 116, respectively, and the area 1 shown in FIG.
The ± 1st-order diffracted lights from 04 are light spots 121 and 12 on the light receiving portions 114 and 115, respectively, as shown in FIG.
5 is formed.

When the levels of the electric signals obtained by photoelectric conversion by all the light receiving sections 109 to 116 are represented by V109 to V116, the focus error signal is {(V109 + V112) by the known Foucault method.
The track error signal obtained from the calculation of − (V110 + V111)} is (V113
It is obtained from the calculation of −V114). The reproduction signal of the disc is obtained from the calculation of (V115 + V116).

Next, a module when the optical head device of the present invention is applied to an optical head device of a rewritable magneto-optical disk will be described. FIG. 14 shows a block diagram of an example of the module in this case. As shown in the figure, this module includes a package 130 containing a semiconductor laser 126, a photodetector 127, and microprisms 128 and 129.
And the polarizing diffraction grating 131 and the hologram optical element 13 provided on the window of the package 130 in the optical path of the laser light emitted from the semiconductor laser 126 with the spacer 133 interposed therebetween.
It consists of two. The polarizing diffraction grating 131 is shown in FIG.
It has a structure similar to that of the polarizing hologram optical element 93 shown in FIG. 1, and functions to pass a part of the ordinary light of the incident light, diffract a part of the incident light, and diffract all of the extraordinary light.

Next, the operation of the module shown in FIG. 14 will be described. In FIG. 14, the laser light emitted from the semiconductor laser 126 passes through the hologram optical element 132 by about 80%.
Is transmitted and enters the polarizing diffraction grating 131 as ordinary light,
About 90% of the light is transmitted to the disc (not shown). On the other hand, of the reflected light from the disc, about 8% of the ordinary light component and about 80% of the extraordinary light component are diffracted by the polarizing diffraction grating 131 as ± first-order diffracted light, of which the + 1st-order diffracted light passes through the micro prism 128. The −1st-order diffracted light is received by the photodetector 127 via the microprism 129. Further, about 90% of the ordinary light component passes through the polarization diffraction grating 131 and enters the hologram optical element 132, and about 16% of ± first-order diffracted light is diffracted and received by the photodetector 127. The mounting form of the semiconductor laser 126 on the photodetector 127 is the same as in FIG.

FIG. 15A is a pattern of interference fringes of the polarization diffraction grating 131 in the module of FIG. 14, FIG. 15B.
Shows respective interference fringe patterns of the hologram optical element 132 in the module of FIG. Polarizing diffraction grating 13
The first optical axis 135 is set in the direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 126. The hologram optical element 132 has a pattern divided into four regions 136 to 139 only near the center as shown in FIG. 15B.

Of the reflected light from the disc, the transmitted light of the polarizing diffraction grating 131 passes through the inside of the regions 136 to 139, and the ± 1st order diffracted light of the polarizing diffraction grating 131 is the castle 136.
Pass through the exterior of ~ 139. The regions 136 and 137 of the hologram optical element 132 have an off-axis concentric circular pattern, and function as a convex lens for + 1st order diffracted light and a concave lens for −1st order diffracted light.

FIG. 16 shows the structure of the micro prism 128 in the module of FIG. Micro prism 128
Are three glass blocks 141, 142 and 143.
Blocks 141 and 142 of the dielectric multilayer film 145
The blocks 142 and 143 are bonded together via the dielectric multilayer film 146.

According to the micro-prism 128 having this structure, the P-polarized component of the incident light 147 is almost completely transmitted through the block 142, the dielectric multilayer film 146 and the block 143 to become the transmitted light 148. On the other hand, the S-polarized component of the incident light 147 is almost completely reflected twice by the dielectric multilayer films 146 and 145, and further passes through the block 142 to become reflected light 149. The structure of the micro prism 129 is similar to that shown in FIG.

FIG. 17 shows an example of the pattern of the light receiving portion of the photodetector 127 in the module shown in FIG. 14 and the arrangement of the light spots on the light receiving portion. In FIG. 17, the photodetector 1
A semiconductor laser 126 is provided at a position slightly below the center of 27, and a mirror 150 for reflecting the emitted light of the semiconductor laser 126 is provided. Further, in the figure, light receiving portions 151 and 152 are provided on the upper left side and light receiving portions 153 and 154 are provided on the lower right side.

Further, in the figure, the light receiving parts 155, 156 and 15 divided into three parts on the left side of the installation position of the mirror 150.
7, and light receiving portions 158, 159 and 160 divided into three parts are arranged on the right side. Further, the light receiving unit 15
5, light receiving parts 161 and 162 are provided on the upper side of FIG.
Are provided, and the light receiving portions 163 and 164 are provided on the lower side of the light receiving portions 157 and 160 in the figure, respectively.

In the photodetector 127, the + 1st order diffracted light from the polarizing diffraction grating 131 shown in FIG. 14 is separated into transmitted light and reflected light as shown in FIG. 16 using the microprism 128 as an analyzer. The transmitted light forms a light spot 171 on the light receiving portion 151 as shown in FIG. 17, and the reflected light forms a light spot 172 on the light receiving portion 152. The -1st-order diffracted light from the polarizing diffraction grating 131 is separated into transmitted light and reflected light by using the microprism 129 as an analyzer, and the transmitted light forms a light spot 173 on the light receiving portion 153 as shown in FIG. Then, the reflected light forms a light spot 174 on the light receiving portion 154.

On the other hand, the hologram optical element 132 shown in FIG.
The + 1st order diffracted light from the regions 136 and 137 shown in (b) is divided into three light receiving portions 155 to 1 as shown in FIG.
57 light spots 175 and 176 are formed on 57,
The −1st-order diffracted light from the regions 136 and 137 is formed into a light spot 1 on each of the three light receiving portions 158 to 160.
77 and 178 are formed. The light receiving units 155 to 157 are located behind the converging point, and the light receiving units 158 to 160 are located in front of the converging point.

The hologram optical element 132 shown in FIG.
The ± first-order diffracted light from the region 138 shown in FIG.
As shown in FIG. 7, light spots 179 and 181 are formed on the light receiving portions 161 and 164, respectively. Further, the ± first-order diffracted light from the region 139 shown in FIG. 15B of the hologram optical element 132 forms light spots 180 and 182 on the light receiving portions 162 and 163, respectively, as shown in FIG.

When the levels of the electric signals obtained by photoelectric conversion by all the light receiving sections 151 to 164 in the photodetector 127 are represented by V151 to V164, respectively, the focus error signal is represented by the known spot size method. (V155 + V157 + V159)-(V1
56 + V158 + V160)}, and the track error signal is {(V1
61 + V164)-(V162 + V163)}. Also, the reproduction signal of the disc is {(V15
1 + V153)-(V152 + V154)}.

The embodiment of the optical head device of the present invention shown in FIG. 1 has a configuration using two modules 11 and 12 each having a semiconductor laser and a detection optical system built therein for downsizing. However, the present invention is not limited to this, and a configuration using two sets of blocks in which a semiconductor laser and a detection optical system are separately provided is also possible.

[0065]

As described above, according to the present invention,
For the first light, the objective lens can be used with an effective numerical aperture determined by the effective diameter of the objective lens and the focal length of the objective lens, and for the second light, the cross section of the light flux passing through the aperture limiting element can be used. Since the objective lens can be used with an effective numerical aperture determined by the diameter and the focal length of the objective lens, the optimum wavelength and the numerical aperture of the objective lens can be selected for each of the two types of optical recording media. Therefore, both two types of optical recording media such as a digital video disc and a compact disc including a write-once type can be reproduced with the optimum wavelength and the numerical aperture of the objective lens.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical head device of the present invention.

2A and 2B are a plan view and a cross-sectional view of an aperture limiting element used in the first embodiment of the optical head device of the present invention.

FIG. 3 is a plan view and a sectional view of an aperture limiting element used in a second embodiment of an optical head device of the present invention.

FIG. 4 is a plan view and a sectional view of an aperture limiting element used in a third embodiment of an optical head device of the present invention.

FIG. 5 is a diagram showing a configuration of a wavelength filter used in the embodiment of the optical head device of the present invention.

FIG. 6 is a diagram showing a module configuration when the embodiment of FIG. 1 is applied to a read-only disc.

FIG. 7 is a diagram showing a mounting form of a semiconductor laser on a photodetector in the module of FIG. 6;

8 is a diagram showing a pattern of interference fringes of a diffraction grating and a hologram optical element in the module of FIG.

9 is a diagram showing an example of a pattern of a light receiving portion of a photodetector and an arrangement of light spots on the light receiving portion in the module of FIG.

FIG. 10 is a diagram showing a configuration of a module when the embodiment of the optical head device of the present invention is applied to a write-once disc or a rewritable phase change disc.

11 is a diagram showing a structure of an example of a polarizing hologram optical element in the module of FIG.

12 is a diagram showing a pattern of interference fringes of the polarization hologram optical element in the module of FIG.

13 is a diagram showing a pattern of a light receiving portion of a photodetector and an arrangement of light spots on the light receiving portion in the module of FIG.

FIG. 14 is a diagram showing the configuration of a module when the embodiment of the optical head device of the present invention is applied to a rewritable magneto-optical disk.

15 is a diagram showing a pattern of interference fringes of a polarizing diffraction grating and a hologram optical element in the module of FIG.

16 is a diagram showing a configuration of a micro prism in the module of FIG.

17 is a diagram showing a pattern of a light receiving portion of the photodetector and an arrangement of light spots on the light receiving portion in the module of FIG.

FIG. 18 is a diagram showing a configuration of an example of a conventional optical head device.

[Explanation of symbols]

11, 12 Module 13, 47 Wavelength filter 14 Collimator lens 15, 25, 31 Aperture limiting element 16 Objective lens 17 Disk 20, 27, 33 Circular groove 21, 28, 34 Substrate 22, 36 Wavelength filter film 23, 39, 98 Phase Compensation film 29, 35, 57 Diffraction grating 37 Adhesive 38 Glass substrate 41, 42, 48-50, 141-143 Block 43, 51, 52, 145, 146 Dielectric multilayer film 44, 45, 147 Incident light 54, 90 , 126 semiconductor laser 55, 91, 127 photodetector 56, 92, 130 package 58, 132 hologram optical element 59, 133 spacer 61 heat sink 62, 64, 70, 107, 150 mirror 63 recess 66, 101-104, 136- 139 area 71-80, 109-116 151-164 Light receiving part 81-86, 118-125, 171-182 Light spot 93 Polarizing hologram optical element 94 1/4 wavelength plate 96 Lithium niobate substrate 97 Proton exchange area 105, 135 Optical axis 128, 129 Micro prism 131 Polarizing diffraction grating 148 Transmitted light 149 Reflected light

Claims (6)

[Claims] 1. A first light source for emitting a first light of a first wavelength, a second light source for emitting a second light of a second wavelength different from the first wavelength, and While the first light from the first light source and the second light from the second light source are multiplexed and guided to the optical recording medium,
Optical multiplexing / demultiplexing means for demultiplexing reflected light from the optical recording medium, and light collected by the optical multiplexing / demultiplexing means is condensed on the optical recording medium and then reflected on the optical recording medium. The objective lens that transmits the reflected light and the optical multiplexing / demultiplexing unit and the objective lens are provided, and all the incident light of the first wavelength is transmitted, and the incident light of the second wavelength is transmitted. Is an aperture limiting element that transmits only the central portion of the beam cross section, a first photodetection optical system that receives the reflected light of the first wavelength that has been demultiplexed by the optical multiplexing / demultiplexing means, and the optical multiplexing / An optical head device comprising: a second photodetection optical system that receives the reflected light of the second wavelength that is demultiplexed by the demultiplexing means. 2. The wavelength limiting film provided only outside a circular region having a diameter smaller than the effective diameter of the objective lens on the substrate, and the phase limiting element provided on the wavelength filtering film. A compensation film, the first light of the first wavelength is almost completely transmitted outside the circular region, and the second light of the second wavelength is almost completely reflected,
2. The optical head device according to claim 1, wherein the light incident on the circular area is configured to completely transmit both the first and second light. 3. The wavelength filter film comprises a high refractive index layer having a thickness of d ₁ and a refractive index of n _{1, and} a low refractive index layer having a thickness of d ₂ and a refractive index of n ₂ which are alternately odd numbers. In a layered construction, and
3. The optical head device according to claim 2, wherein the optical head device has a relationship satisfying an equation of n ₁ · d ₁ = n ₂ · d ₂ = λ / 4, where λ is the second wavelength. 4. The aperture limiting element comprises a diffraction grating formed on a substrate only outside a circular region having a diameter smaller than the effective diameter of the objective lens, the diffraction grating having the first wavelength. The first light is completely transmitted, the second light of the second wavelength is almost diffracted, and the light incident on the circular region is completely transmitted by both the first and second light. The optical head device according to claim 1, wherein: 5. The aperture limiting element comprises a diffraction grating and a wavelength filter film on a first substrate, and a phase compensation film on a second substrate, the circular region having a diameter smaller than an effective diameter of the objective lens. Is sequentially laminated only on the outer side of the second
Is filled with an adhesive between the substrate and the wavelength filter film, the first light of the first wavelength is completely transmitted outside the circular region, and the second light of the second wavelength is transmitted. 2. The optical head device according to claim 1, wherein the optical head device is configured to completely reflect and diffract light, and to completely transmit both the first and second light incident on the circular region. 6. The wavelength filter film comprises a high refractive index layer having a thickness of d ₁ and a refractive index of n _{1, and} a low refractive index layer having a thickness of d ₂ and a refractive index of n ₂ alternately. It is a structure in which an odd number of layers are deposited on the diffraction grating, and has a relationship satisfying the following equation, where n ₁ · d ₁ = n ₂ · d ₂ = λ / 4, where λ is the second wavelength. The optical head device according to claim 5, wherein: